Adim: A Diminished Piano Chord

Root position: either hand, fingers low note to high
Hand	Notes	Fingers
Right	A, C, E♭	1-3-5
Left	A, C, E♭	5-3-1

Scale degree, note, and interval measured from the root.
Degree	Note	Interval from root	Semitones
1	A	Perfect unison	0
♭3	C	Minor third	3
♭5	E♭	Tritone	6

Construction

A Diminished = Root + Minor 3rd + Diminished 5th = A, C, E♭

Note	Interval	Degree
A	Root	1
C	Minor 3rd	♭3
E♭	Diminished 5th	♭5

Fingering

Note	Key color	Right hand	Left hand
A	white	thumb (1)	little finger (5)
C	white	middle finger (3)	middle finger (3)
E♭	black	little finger (5)	thumb (1)

Right hand: thumb (1) on A, middle finger (3) on C, little finger (5) on E♭.

Left hand: little finger (5) on A, middle finger (3) on C, thumb (1) on E♭.

A Diminished Inversions

Root position
A – C – E♭
1st inversion (Adim/C)
C – E♭ – A
2nd inversion (Adim/E♭)
E♭ – A – C

Key Signature

A Diminished chord is built from symmetrical or ambiguous intervals, so it doesn't belong to a single key and has no key signature of its own.

Chords in the Key of A Major

These are the triads built on each degree of A Major:

I — A Major (major)

Degree	Numeral	Chord	Quality
1	I	A Major	Major
2	ii	B Minor	Minor
3	iii	C♯ Minor	Minor
4	IV	D Major	Major
5	V	E Major	Major
6	vi	F♯ Minor	Minor
7	vii°	G♯ Diminished	Diminished

How A Diminished functions in a key

The same chord takes on a different harmonic role depending on the key it appears in. Here is where A Diminished sits diatonically across the common keys:

In B♭ major, A Diminished is the vii° chord — the dominant.
In G minor, A Diminished is the ii° chord — a predominant.

Scales That Include the A Diminished

Bb Major (vii°)
G Minor (ii°)
C Dorian (vi°)
D Phrygian (v°)
Eb Lydian (#iv°)
F Mixolydian (iii°)
G Aeolian (ii°)
A Locrian (i°)

A Diminished : Frequently Asked Questions

What is the A Diminished chord on piano?

The A Diminished chord contains the notes A – C – E♭. On piano, play these notes together to sound the chord.

What notes are in the A Diminished chord?

The A Diminished chord contains: A (root), C (minor third), and Eb (diminished fifth). Both intervals are compressed: the minor third is 3 semitones above the root, and the diminished fifth is 6 semitones, a tritone.

How does A Diminished differ from A Minor?

A Minor has a perfect fifth. A Diminished lowers the fifth by one semitone to Eb (diminished fifth). That extra compression creates intense harmonic tension: the tritone between root and diminished fifth is the most dissonant interval in Western music.

What is the symbol for the A Diminished?

A Diminished is written as Adim or A°. The ° or "dim" symbol means both the third and fifth are minor/diminished. Do not confuse with Adim7 or Aø (half-diminished), which include additional notes.

What are the inversions of A Diminished?

First inversion (A Diminished/C): C–Eb–A. Second inversion (A Diminished/Eb): Eb–A–C. Diminished triads are used in classical music as the vii° chord, the chord one semitone below the tonic, with strong resolution pull.

How is A Diminished used in music?

A Diminished most commonly functions as the vii° chord in a major key, creating strong resolution back to the tonic. It also works as a chromatic passing chord between two nearby chords, and in classical music as a brief point of dissonance. Jazz uses the full four-note dim7 more often than the triad.

What songs use diminished chords?

Michelle (Beatles) uses a diminished chord as a chromatic passing chord. Many classical pieces use vii°–I cadences. Jazz standards use dim7 chords as chromatic passing and approach chords. Diminished harmony also appears in flamenco and film music for dramatic tension.

A Diminished in detail

Exact

Every pitch class is present and nothing outside the chord is added.

Type	Notes	Semitones	Span	Omissions and additions	Set relation
Close, root position	A3 C4 E♭4	6	83 mm	none	identical
Close, first inversion	C4 E♭4 A4	9	124 mm	none	identical
Close, second inversion	E♭4 A4 C5	9	124 mm	none	identical
Open, fifth on top	A2 E♭3 C4	15	206 mm	none	identical

Reduced

A subset of the pitch classes: the identity is incomplete rather than altered.

Type	Notes	Semitones	Span	Omissions and additions	Set relation	Fit
Root and third only	A3 C4	3	41 mm	omits E♭	subset

Spans are measured centre to centre at a 165 mm octave (standard keyboard geometry).

Position	Bass note	Notes in order	Figured bass	Semitones	Span
Root position	A	A3, C4, E♭4	5/3	6	83 mm
First inversion: Adim/C	C	C4, E♭4, A4	6/3	9	124 mm
Second inversion: Adim/E♭	E♭	E♭4, A4, C5	6/4	9	124 mm

One position per chord tone in the bass. Spans are for close position: voiced inversions appear under Voicings.

Progression	Key	Role	Sequence	Voice leading
ii°, v, i	G minor	ii°	Adim to Dm to Gm	Adim opens the phrase
vii°, I	B♭ major	vii°	Adim to B♭	Adim opens the phrase

Root motion, common tones and voice displacement are computed from pitch class sets. Roman numerals follow common practice functional harmony.

Which keys it belongs to

Key	Roman numeral	Function
G minor	ii°	Predominant
B♭ major	vii°	Dominant function

Classification system: common-practice functional harmony.

Change one note

Chords a single note away, and what moving that note does.

Chord	Change	Formula	Common tones
Am7♭5	adds G	1 ♭3 ♭5 ♭7	3
Adim7	adds G♭	1 ♭3 ♭5 ♭♭7	3
Am	E♭ becomes E	1 ♭3 5	2
Am7	E♭ becomes E, G	1 ♭3 5 ♭7	2
AmMaj7	E♭ becomes E, G♯	1 ♭3 5 7	2
Am6	E♭ becomes E, F♯	1 ♭3 5 6	2
A	C, E♭ becomes C♯, E	1 3 5	1
Aaug	C, E♭ becomes C♯, E♯	1 3 ♯5	1
Asus2	C, E♭ becomes B, E	1 2 5	1
Asus4	C, E♭ becomes D, E	1 4 5	1

Frequencies

Note	MIDI	Frequency
A3	57	220.00 Hz
C4	60	261.63 Hz
E♭4	63	311.13 Hz

Reference pitch A440, 12-TET, close root position.

Set theory: prime form, Forte number, interval vector

Absolute pitch class set: {9, 0, 3}
Normal order: [9, 0, 3]
Prime form: (036)
Forte number: 3-10
Interval vector: <002001>

Pair	Interval	Semitones	Interval class
A to C	Minor third	3	3
A to E♭	Tritone	6	6
C to E♭	Minor third	3	3

Where these facts come from

Every value on this page is derived from the note formula for a diminished applied to the root A, using standard music theory. Nothing here is hand-entered per chord, so the notes, intervals, inversions and frequencies cannot drift out of agreement with each other. Pitches assume 12-TET at A440.

A Diminished

Fingerings

A Diminished: notes and degrees